The present invention relates generally to the art of cutting tools, and particularly to shearing devices, such as loppers.
The starting point of the lopper of the present invention, and thus the lopper according to the most closely-related background art related thereto, is disclosed in U.S. Pat. No. 5,950,315. Since most of the structural features of the lopper of the present invention correspond with those of the lopper disclosed in the above patent, it is incorporated herein by reference.
In the lopper known from the above patent, a spring-biased cutting blade which is pivotally turnable about a pivot point and which, together with a fixedly-positioned counter-blade, constitutes a jaw, is used by a drive mechanism which, through a chain, transmits power to the cutting blade. In the drive mechanism, the chain is attached to a chain wheel connected to a drive wheel connected to a driving line. A length of the driving line has been wound around the drive wheel. The chain wheel and the drive wheel are arranged to rotate together around a common axis, and when the driving line is drawn, both the drive wheel and the chain wheel connected thereto are made to rotate around their common axis. When the driving line is no longer drawn, the spring of the blade returns the driving line into its original position. Such a drive mechanism is simple and reliable.
The above-described drive mechanism does, however, have a problem. In the lopper described in the above-mentioned U.S. Pat. No. 5,950,315, the lopping head is further pivotally mounted relative to the elongate housing of the lopper to enable the angle of the lopping head to be adjusted with respect to the elongate housing. Such adjustment causes the driving line either to wind around the drive wheel or to be released therefrom. If the driving line winds, around the driving wheel, it simultaneously also winds the chain wheel which, in turn, directs a pulling force at the moving blade through the chain, changing the width of the jaw. In order for this change to be compensated for or cancelled out, the attachment at one end of the driving line to the elongate housing of the lopper has to be released, thus releasing more driving line in order to enable the maximum dimensions of the jaw to be returned. Even if this adjustment of the length of the driving line could be carried out in a simple manner with respect to the knot by which the driving line has been attached to the elongate housing, the fact that the length of the driving line is being adjusted nevertheless causes some additional inconvenience.
An object of the present invention is thus to further develop the lopper described in the above-mentioned U.S. Patent in such a way that the drive mechanism automatically compensates for the length of the driving line in order to enable the position of the lopping head to be adjusted relative to the elongate housing without the adjustment affecting the width of the jaw. This enables the need to adjust the dimensions of the jaw by adjusting the length of the driving line to be eliminated.
The above-mentioned object is achieved by means of a lopper according to the invention, the lopper comprising:
a lopping head having a spring-biased blade pivotally connected to a jaw about a pivot point, the jaw cooperating with the blade to sever a workpiece received in a bight formed by the jaw;
a drive mechanism connected to the lopping head;
an elongate housing connected to the drive mechanism;
the drive mechanism comprising:
a first and a second mating portion selectively rotatable with respect to one another about an axis permitting positioning of the lopping head relative to the elongate housing, the first mating portion being connected to the elongate housing and the second mating portion being connected to the lopping head;
a first wheel rotatable about the axis;
a second wheel rotatable about the axis and coupled to the blade by a head line, the head line being connected to the second wheel at a first connecting point such that the head line is wound about a guiding surface of the second wheel as the second wheel rotates about the axis; and
a driving line arrangement comprising a driving line arranged to rotate the second wheel and the first wheel together when the driving line is drawn and to keep the second wheel stationary when the lopping head is positioned relative to the elongate housing.
According to a preferred embodiment of the invention, the driving line arrangement comprises:
a through hole in the second wheel for allowing the driving line to, be led through the second wheel,
a first passage on the inner surface of the second mating portion for receiving a first portion of the driving line led through the second wheel, the first portion of the driving line sliding through the hole when the first and second wheel rotate together,
a second passage in the second mating portion for leading the driving line outside the second mating portion, the second passage turning with the second mating portion when the lopping head is positioned relative to the elongate housing, and
a third passage on the first, mating portion for receiving a second portion of the driving line, one end of the second portion of the driving line being at a second connecting point connected to the first mating portion and the length of the second portion of the driving line depending on the position of the lopping head relative to the elongate housing.
As is apparent from the above, the drive mechanism of the lopper of the invention has two operating states, one being the operating state prevailing when the lopper is used in an ordinary manner, and the other being the operating state prevailing when the angle of the lopping head is being adjusted with respect to the elongate housing. Both of these operating situations require that the length of the driving line should be compensated for separately from each other in order for the drive mechanism to operate as desired and to allow the position of the lopping head to be adjusted relative to the elongate housing without causing a need to adjust the length of the driving line in order to keep the dimensions of the jaw as desired.